docs: def repmat(x, r, c):
      '''
      repmat(x, r, c) is equivalent to numpy.matlib.repmat(x, r, c) except that it works correctly for
        sparse matrices.
      '''
      if sps.issparse(x):
          row = sps.hstack([x for _ in range(c)])
          return sps.vstack([row for _ in range(r)], format=x.format)
      else: return np.matlib.repmat(x, r, c)